The present invention relates to backing for transducers. In particular, an acoustic absorber is provided as a backing material.
Ultrasound transducers, such as used in medical diagnostic ultrasound imaging, include transducer elements for converting between electrical and acoustic energy. The transducer elements are manufactured to be positioned adjacent to a patient. Ultrasound energy travels from the transducer element through one or more matching layers into the patient. Responsive echos are then received by the transducers. When the transducer elements generate acoustic energy, the acoustic energy propagates from the element both towards and away from the patient due to expansion and contraction of the elements, generally along one dimension. The acoustic energy propagation towards the patient is desired; the acoustic energy propagating away from the patient is undesired. To absorb the undesired acoustic energy and prevent receiving echoes from clutter or structures outside of the patient, an acoustically absorptive backing block connects to the transducer.
Backing blocks include attenuative material for absorbing acoustic energy. Backing blocks are also frequently used as a rigid or semi-rigid support for the assembly of the ultrasound transducer stack of the transducer material and associated matching layers. For example, plasticized resins, such as epoxies, are used, because they can be both rigid and acoustically absorbing. Plasticizers are non-volatile solvents that increase the attenuation of the resin, based on intermolecular interaction. However, the plasticizer lowers the glass transition temperature, softening the resin on a microscopic level. Such resins are somewhat but generally not highly absorptive of ultrasound, and are somewhat but not particularly rigid. In practice, a balance is struck between rigidity and attenuation to make an acceptable transducer backer block. The balance may yield material that is marginally functional for both purposes. Rigid urethanes or polyesters have also been used for backing block materials.
Sound absorbers for walls have used different materials in combination to absorb sound. For example, lead spheres are coated with rubber and placed within an epoxy or foam. The lead is bonded to the rubber, and the rubber is bonded to the epoxy. Acoustic energy is then absorbed through relative motion of the ball bearings as compared with the epoxy matrix.